The present invention relates to methods for direct synthesis of transition metal carbonitrides, in particular titanium carbonitride.
Transition metal carbides, nitrides, and carbonitrides are of practical interest because of their hardness, corrosion resistance, and thermal stability. Furthermore, cermets of titanium carbide/nickel and titanium carbonitride/nickel are considered excellent substitutes for tungsten carbide/cobalt cermets; nickel is more abundant and less expensive than cobalt.
Three approaches have heretofore been employed to produce TiC, TiN, and titanium carbonitride (TiC.sub.x N.sub.y). One route calls for direct chemical reduction of titanium oxide, titanium chloride, and titanium hydride by carbon, nitrogen, and ammonia, or by carbon and nitrogen to form TiC, TiN and TiC.sub.x N.sub.y. Another approach involves solid state diffusion of C, N or both into Ti powders at high temperatures (1000.degree.-1500.degree. C.) in a reaction taking place over the course of several hours, or by sintering a mixture of TiC and TiN. These approaches generally involve three steps: formation of the carbide and nitride phases separately, followed by a homogenizing process in which these two phases are reacted at high temperature.
A third known route is self-propagating high-temperature synthesis (SHS) or combustion synthesis which has been used for TiC [J. B. Holt and Z. A. Munir, "Combustion Synthesis of Titanium Carbide: Theory and Experiment, " J. Mater. Sci., 21(1), 251-9 (1986); A. G. Merzhanov and I. P. Borovinskaya, "Self-Propagating High Temperature Synthesis of Refractory Inorganic Compounds," Dokl. Akad. Nauk. SSSR (Chem.), 204, 429-32 (1972); A. I. Kirdyashkin, Yu. M. Maksimov, and E. A. Nekrasov, "Titanium-Carbon Interaction Mechanism in a Combustion Wave," Fizika Goreniya i Vzryva (Translation), 17(4), 33-6 (1981); O. Yamada, Y. Miyamoto, and M. Koizumi, "High Pressure Self-Combustion Sintering of Titanium Carbide," J. Am. Ceram. Soc., 70(9), C206-8 (1987)], TiN [S. L. Kharatyan, Y. S. Grigorev, and A. G. Merzhanov, "Ignition of Titanium in Nitrogen," Comb. Explo. Shock Waves, 11, 21-6 (1975); Z. A. Munir, S. Deevi, and M. Eslamloo-Grami, "The Synthesis of Titanium Nitride by Self-Sustaining Combustion Method," High Temperatures-High Pressures, 20, 19-24 (1988); M. Eslamloo-Grami and Z. A. Munir, "Effect of Porosity on the Combustion Synthesis of Titanium Nitride," J. Am. Ceram. Soc., 73(5), 1235-9 (1990); M. Eslamloo-Grami and Z. A. Munir, "Effect of Nitrogen Pressure and Diluent Content on the Combustion Synthesis of Titanium Nitride, " J. Am. Ceram. Soc., 73(8), 2222-7 (1990); S. Deevi and Z. A. Munir, "The Mechanism of Synthesis of Titanium Nitride by Self-Sustaining Reactions", J. Mater. Res., 5(10), 2177-83 (1990)], and TiCN [A. B. Avakian et al., "Synthesis of Carbonitrides of Transition Metals," in Combustion Process in Chemical Technology and Metallurgy, Chernogolovka, 1975]. In the SHS process, the highly exothermic heat of reaction propagates in the form of a combustion wave through the reactants, converting them into product phases. While production of TiC and TiN by the SHS method has already been studied extensively, research on TiC.sub.x N.sub.y by this method has been limited. The primary focus in the reported study of combustion synthesis of TiC.sub.x N.sub.y [Avakian et al., supra] was on the use of liquid nitrogen as a reactant.
It is an object of the present invention to provide improved methods for the synthesis of transition metal carbonitrides.